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[IMG] Turning threads in steel: badly torn finish with ground and honed HSS

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  • [IMG] Turning threads in steel: badly torn finish with ground and honed HSS



    Pictured is a typical example from today, M16x1.5 near side, M18x2.5 far side. Regular, round turning with carbide inserts leave a very beautiful finish most of the time, and also when threading with 11IR carbide inserts held in boring bars. This is on my nearly 2 metric ton 1980 TOS SN50B x 1500 mm. from the wonderful socialist paradise state of Czechoslovakia (now defunct).

    I try to be careful with workpiece overhang and often use the tailstock for support. The problem only exist in general purpose low carbon steels S235, S275, S355 and St. 52, equivalent to about AISI 1018 through ASTM A36 and A572 grade 50; I've not yet had the pleasure trying to thread stainless steel or the chromium-molybdenum kinds. Almost all the work I do is in mild steel, and the thread cutting problem does not manifest in aluminium or brass at all, that I've seen. I'm using flank infeed at 29.5° angle as measured off the X-axis and near ~0.05-0.02 mm. finishing infeed dialed in on the compound slide. I'd like to try some lead/sulfur free-machining steel, but have none at hand that I can readily identify with certainty.

    I've got the threading tool ground with around 10° side rake, no back rake and what I believe to be a generous side relief angle, yet still I'm leaning towards the possibility of not having enough relief angle on the tool? I guess more experimentation is on the agenda for the next 5-year plan.



    Bonus round: I know you gentlemen love seeing pictures of our decadent filth and depraved equipment hoarding, so here's a recent one, showing my new old 1.4 ton TOS BPH 20 surface grinder from 1975 and the rear of my 1956 Ferguson 35 tractor with the 2.3-liter 4-cylinder Standard Motor Company diesel engine. The surface grinder was supplied with a magnetic chuck from Eclipse in England, an external coolant pump and tank and also three 250 mm./10-inch grinding wheels, one of which I've been able to identify as for grinding hardened steel. It's blueish in color, and two others are vitrified, open structure and pink.


  • #2
    Soft gummy steel can do that.
    2730

    Keep eye on ball.
    Hashim Khan


    It's just a box of rain, I don't know who put it there.

    Comment


    • #3
      A. What cutting oil you are using when threading? Spindle rpm?
      B. Can you post pic of your HSS threading tool? It needs to be absolutely sharp.

      Solution C. is to buy cheapish 16ER carbide inserts and tool holder but this HSS thing should be sorted out also..
      https://www.ebay.com/itm/10PCS-IN-BO...YAAOSwmmxW6SPU
      Location: Helsinki, Finland, Europe

      Comment


      • #4
        • Using CRC Supercut II cutting fluid.
        • Speed was about 125 RPM.
        • Good call on this perhaps being a material problem.
        • Great call on getting more tools, I've been looking at a 16ER solution for some time now.
        • Cutting tool is honed with a diamond lap to a appreciably bright cutting edge.

        CRC Supercut II

        EDIT: Tool pictures tomorrow, will dust off my macro lens for my DSLR.

        Comment


        • #5
          Originally posted by Oyvind Ryeng View Post
          ...[*]Cutting tool is honed with a diamond lap to a appreciably bright cutting edge.
          ,,,,
          I suspect I know what you mean, but just in case; a sharp edge actually disappears. It is only dull edges that show any shiny or bright line etc at the actual edge itself.
          2730

          Keep eye on ball.
          Hashim Khan


          It's just a box of rain, I don't know who put it there.

          Comment


          • #6
            Supercut II is what I was also using until I get allergic to it. Speed sounds reasonable but you could try and see what happens if you drop the speed really slow.

            Material is part of the problem but in my experience the VP15TF coated Mitsubishi inserts work very nicely also on S355 cold drawn bar stock that is common here in Europe.

            If you hone hand-held with diamond lap its also possible that you get slight radius on the cutting edge so that its not really sharp. Depends how good your technique is. I have seen it happen to "my friend" but I'm of course not such a clumsy bastard.
            Or your HSS is some crap quality chinese import, "my friend" had also that.
            Location: Helsinki, Finland, Europe

            Comment


            • #7
              You might try to find the local equivalent of 1215 alloy. It's the easiest, cleanest cutting low carbon steel I've found so far.
              Kansas City area

              Comment


              • #8
                or any of the leaded steels, like 12L14 etc

                Comment


                • #9
                  My take is that the tool needs about 10* of top rake for this gummy stuff. That's been my experience anyway. I have a tool for this stuff with the top rake going away from the left cutting edge. I don't care much about the right 'cutting' edge because it never cuts! With the compound at 29.5* I feed in with the compound only thus I'm always cutting with a high rake tool. The old lard/sulfur oil is my go to for this. Good threads every time...

                  Cheers,
                  Pete
                  1973 SB 10K .
                  BenchMaster mill.

                  Comment


                  • #10
                    Definitely related to the material, it looks just like threading cold rolled steel at low speeds. Several things occur to me:
                    1. Increase RPM (I know, it gets scary).
                    2. Sulphurized cutting oil.
                    3. Stress relieving or annealing with a torch.
                    4. Using hot-rolled 1020, 1215, 12L14 (if it's still available), 1144 (Stressproof), or even 303 stainless.
                    5. Lapping the tool seems like over-kill and may be counter-productive. The fine grooves in a ground cutting edge can act as tiny chip breakers.
                    It's all mind over matter.
                    If you don't mind, it don't matter.

                    Comment


                    • #11
                      I was thinking top rake too .. it looks like its not cutting freely..
                      What method do you use for centre height ?
                      I feed straight in on all my threading and finish is rarely an issue.

                      Comment


                      • #12
                        It seems to me that you might be cutting too shallow. Look at the page https://www.sandvik.coromant.com/en-...s/default.aspx to see what Sandvik recommends.

                        In the case of the 1.5 mm pitch, Sandvik was calling for 6 passes of decreasing depth, starting with .23mm and finishing with .010mm.

                        Dan
                        At the end of the project, there is a profound difference between spare parts and left over parts.

                        Location: SF East Bay.

                        Comment


                        • #13
                          Originally posted by lakeside53 View Post
                          or any of the leaded steels, like 12L14 etc
                          12L14 or 1215 equivalents are hard in here to find. Hardly anyone stocks it or is willing to deal with small customers.

                          Calcinated Imatra M-steels are reasonably nice to work with:
                          http://www.ovako.com/Products/M-Steel/
                          Imatra 4M ( close to 1045), or MOC 410M (4140 prehard)
                          Location: Helsinki, Finland, Europe

                          Comment


                          • #14
                            Nothing wrong with it lovely bit of rebar.
                            Looking at the marks it looks almost like a chatter type of thing as well, tool rigid?
                            Mark

                            Comment


                            • #15
                              well it is why they call 12L14 screw stock - I can be difficult getting good finishes with the broad cut threading requires, in gummy materials. The only way I've been able to get through tear out like that in threading is super sharp hss tools - not quite a mirror as a wood worker would but almost - head in the that direction. Use heavy cutting oil, light cut and as slow as the lathe will go. Slow is the key, with oil and a super sharp tool.....think of scraping, where a super sharp tool going very slowly will make a shiny cut in otherwise difficult to machine steels. My suggestion is toward trying to replicate those cut dynamics
                              Last edited by Mcgyver; 11-10-2017, 08:34 AM.
                              in Toronto Ontario - where are you?

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